Sheet for the manufacture of viscose



Sept. 23, 1930.

G. w. BLANCTO ET'AL SHEET FOR THE MANUFACTURE OF VISCOSE Filed Nov. 2

6000000 716 ooooo'oo ooooooc/ lNVENTOR 5* /fium Patented fiept. 23,E933? GALO W. ECO AND CLETON HENN'INGSEN, OF BUFFALO, NEW YORK,ASSIGNQRE,

BY MESNE ASSIGNMENTS, T0 DU FONT RAYON COMP, QF NEW Y0 CORPUEATION OFDELAWARE SHEET FOR THE MANUFACTURE 0F VISCQSE Application filed.November 4,, 1927. Serial No; 231,090.

In manufacturing viscose the common practice is to place sheets of woodpulp in a steeping press into which caustic solution is admitted, thisforming the first step in the process. After the sheets are thoroughlysteeped, they are compressed to squeeze out the excess caustic liquor.Fhis liquor contains a certain amount of hemi-celluloses which areextracted from the pulp. By the term hemi-celluloses is generally meantthat portion of the pulp which is most closely saccharides.

related in chemical constitution to the large class of compounds knownas sugars or poly- No definite chemical formula can be assigned to thehemi-celluloses, as they are rather variable mixtures of compounds whoseexact constitution is in many cases unknown. It has been customary tostop the operation of the press after a certain travel of the pistontermed the cut-oil, and to permit the liquor extracted up to this timeto return to the source of supply for reuse. 1 The press has been thenput into operation again to extract the remaining liquor which isallowed to flow to waste. This operation has been followed because ofthe fact that the wasted liquor has been found to contain relativelyhigh percentages (2% and over) of hemicelluloses. It hemi-cellulosesaroused in the steeping solution in large percentages, a number of browngelatinized areas will appear,

not only on the surface of the sheets, but extending through the sheetsas well. These areas increase in number in proportion to the increase ofhemi-cellulo'ses in the steeping liquor.

, form cellulose xanthate, the elatinized areas fail to react normallyto the i-sulphide. As

a result of the poor xanthation the subsequent solution in water isincomplete and thus the viscose tends to retain the slimy aggregatewhich soon plugs up to a very undesirable passed before filtering.Charges which ordinarily are screened in a normal period would requirethree or four times as long to screen, when brown gelatinized areas wereformed during steeping. It is, therefore, the custom to keep thepercentage of hemi-celluloses in the caustic liquor below 5% or at themost 1%; This means that the cut-ofi in the steep ing tank must be setat a point which results in the waste of about one-third to one-half ofthe caustic employed in the press. Many schemes have been suggested toreclaim and reuse the wasted liquor most of which are expensive andunsatisfactory.

Therefore, one of the objects of our invention is to provide a methodand a means which shall avoid the necessity of adopting such expensivemethods as referred to above and which shall at the same time permit thereuse of 100% of the caustic liquor which has formerly been wasted.

It has been found that, when all of the caustic liquor is returned tothe make-up tank from the steeping press, the hemi-celluloses containedtherein will gradually build up to about 3.5% and over. The percentagedepends on the specific pulp used and may run very high. A highpercentage of hemi-celluloss, however, has been accompanied with anincrease in brown gelatinized areas referred to above, often as many as75% of the sheets of pulp developing these areas. These areas cause thetrouble in shredding xanthation and filtration referred to above.

It has been observed, however, that the finished rayon is not harmed bythe presence of the hemi-celluloses in the caustic liquor. The troublewas caused almost entirely in the operating steps.

Another object of our invention, therefore, is to provide a novel andimproved means which shall permit the use of a steeping causticcontaining relatively high percentages of hemi-celluloses and whichshall thus avoid the necessity of wasting such a large amount ofsteeping liquor.

In the accompanying drawing in which we have shown certain means forpracticing our invention:

Figure 1 is a diagrammatic plan view showing a steeping press, the tankbeing shown in section.

Figures 2 to 5 inclusive show various means by which our invention maybe practiced.

Figure 6 is a section on the line 6'6 of Fi ure 5,

eferring now to the drawings in detail and more particularly to Figure1, the numeral 1 designates the steeping tank of the pressin which theraw material, in this case sheets of wood pulp, is deposited fortreatment by a bath of caustic solution. The sheets of pulp aredesignated 2 and are ar-. ranged on edge between perforated iron plates3, which hold the sheets upright. From five to twenty sheets of pulp areusually placed in a compartment formed between two plates and the numberof compartments is determined by the size of the particular apparatusemployed, and may range from ten to one hundred. For the purpose ofillustration, however, and in order to better show the invention on alarge scale, we have shown the space taken up by a compartment as beingsomewhat exaggerated. The object of the iron plates is to hold the pulpsheets upright and allow drainage of the liquor.

The caustic solution is supplied from the make-up tank 4 and the flow ofthe press 1 is controlled by the valve 5. An outlet 6 is provided fromthe other end of the tank and this outlet is provided with a connection7 leading back to the make-up tank 4 and controlled bya valve 8, andalso with a connection 9 through which the solution may be wasted, thisconnection being controlled by the valve 10. Slidably mounted in one endof the tank 1 is a piston rod 11 having ahead 12 contacting with thecontents of the press. The rod may be operated by any suitable means tocompress the pulp.

In operation a solution of caustic soda of a normal strength of about15% to 30% is maintained in the make-up tank, and this solution is runinto the press through the valve 5 and to a height which will completelysubmerge all of the sheets 2. The sheets are left in the solution for aperiod which may vary from about 30 minutes to several hours in order tobecome thoroughly soaked therewith. Then the press is emptied of theexcess solution or liquor by opening the valve 8 and permitting the linor to run back to the tank 4, the valve 10 0 course being closed. Thepiston is then moved until the head reaches some such point as thatindicated by the arrow C, the length of travel of'the' piston head beingtermed the cut-off. The liquor which is pressed out of the caustic bythis actuation of the iston is low in hemi-celluloses, and it has eenthe ractice to permit this liquor to return to t e make-up tank.

The remaining liquor is relatively high in hemi-celluloses and thereforeit has .been the practice to waste it. Therefore, the next step in theoperation has been to close the valve 8 and open the valve 10, afterwhich the piston is again actuated to press out the remaining liquorfrom the pulp. The cut-off has been determined by the amount ofhemi-cellulose content which it has'been possible to use in the steepingliquor without producing the undesirable brown areas to such an extentas to make filtration diflicult. As pointed out above this content hasbeen kept at about .5%, or at most 1%, and, when the cut-off has beenset so as to maintain this percentage of 'hemi-celluloses, the resultingwaste 'of liquor has been large.

We have found that the brown gelatinized areas referred to above form onthose por-. tions of the pulp sheets which do not have free access tothe caustic solution. .The pulp absorbs the caustic soda out of thesolution with great rapidity. The result is that the pulp to which thecaustic solution has free access absorbs the caustic from the solutionbefore the solution reaches that part of the pulp to' which access ismore diflicult. Thus, in a relatively short time the concentration ofthe solution is substantially reduced. At the same time the pulp inthese localized areas does not react normally to the causticv soda,since the concentration of'the solution with which it is in contact hasbeen materially reduced before it reaches these areas. This conditionresults in the formation of the brown areas. It has beenfound that afterbrown areas have once been produced, subsequent steeping in caustic ofnormal strengtheven for long periods of time will not serve ,toeliminate them. In other words, the pulp rate at which diffusion of thecaustic to the interior portions of the sheets will take place. Thus, itbecomes increasingly difiicult for solutionsof higher viscosity (that isthose containing large percentages of hemi-celluloses) to penetratecompletely between and into the sheets as ordinarily placed in thesteeping press.

\Vhen the sheets of pulp are wetted with the steeping solution theyswell very rapidly. This swellin tends to press the sheets more closelytoge her and tends to make the access be returned to the make-up tankfor reuse.

arrests before swelling, the brown gelatinized areas loses which arecarried down in the are not formed. Experiments disclosed the fact thata solution containing a high content of hemi-celluloses then could beused without the brown areas occurring. Therefore, by adopting means toinsure that the caustic solution reaches all parts of the sheets beforethey swell, the objectionable gelatinized areas are avoided and all thecaustic solution may The saving in this respect alone is large asindicated above. It was found that the increased percentages ofhemi-celluloses were not only unobjectionable so far as the finishedrayon is concerned but that, it the brown gelatinized areas wereavoided, the soaking and subsequent operations were not adverselyafiected by the presence of the hemi-celluloses.

Another feature of very great importance that has been discovered isthat the high content of hemi-celluloses materially decreases the timenecessary for ripening of viscose. When operating with caustic having ahigh concentration of hemi-celluloses, the ri ening time of viscose isdecreased as muc as It is believed that this is due to the presence ofsmall quantities of hemi-cellu- P p from the steeping operation into theviscose. The time for ripening is usually severaldays, and, as by ourreduced by approximately one-half, the resulting saving is large.

We have-found that another way to reduce the time necessary to ripen theviscose is to ducing reduced.

introducehemi-celluloses into the viscose before the ripening step takesplace. By introhemi-celluloses in this manner also the time of ripeningcan be very materially If desired, the reduction in time may be causedentirely by the hemi-celluloses left over from the steeping-operation orthis may be supplemented as desired bv the addition at extra quantities.Or, if esired, the steeping process may be carried on in the old mannerand hemi-celluloses may be introduced independently of the steepingoperation.

The means for insuring a complete and thorough wetting of the pulp maytake a variety of forms. lln Figures'2 to 6 inclusive we have shown thevarious means which have been tried with success and others will nodoubt suggest themselves to those skilled in the art j @ne means whichhas been found to be ver successful is the provision of the sheets withcorrugations. The corrugations may be arinvention the time has been.

ranged as desired but we have found that, when they are arrangeddiagonally to each edge of the sheet as indicated at 13 in Figure 2, thebest results are obtained. If the corrugations are arranged horizontallyas shown at 14 in Figure 3, excellent results are also obtained. If thecorrugations are arranged vertically as shown at 15 in Figure 4, goodresults are also obtained, although not so good as when they arearranged as shown in Figures 2 and 3.

Another means is indicated in Figures 5 and 6 wherein is shown aplurality of dimples 16 formed by running the sheets through a suitablemachine.

When any one of the embodiments illustrated is employed, it is notnecessary that every sheet shall be constructed as shown.

We have found that it is sufiicient to have, for example eve other sheetmade in special form to insure lice flow of caustic between the sheets.We have shown a number of means for achieving this object but obviouslyother forms also may be developed by those skilled in the art withoutdeparting from the scope of our invention. Obviously, also, it ispossible to insure the thorough Wetting by separately depositing sheetsof pulp or other raw material in the caustic. This operation, however,is dangerous to the operators because of the likelihood of splashing. For that reason this method is undesirable.

In practicing our invention the sheets of raw material are placed in thesteeping press in the compartments as is usual. The corrugations orother means used in place thereof will temporarily hold the sheets inposition so that the greater portions thereof will be exposed to theaction of the steeping liquor. The steeping liquor is then permitted toenter the press. The sheets swell rapidly as the liquor comes in contacttherewith, but the means which we employ permit the liquor to come intocontact with all portions of the sheets and thoroughly saturate thembefore they swell and come in contact with one an other throughout theirsurfaces. After the material is thoroughly steeped, the piston then isactuated to press the material and to extract therefrom the excessliquor, all the liquor thus extracted being returned to the make-up tankfor reuse.

While we have referred to the raw material as being made of wood pulp,it is obvious that our invention may be practiced with any other kind ofraw material to which it is applicable. We are aware that variousmodifications and changes may be made in the practice of our inventionas disclosed in thisapplication and without departing from v the scopeor our invention. We therefore do not intend to limit ourselves exceptby the appended claims.

e claim:

l. A sheet composed of wood pulp from ill which viscose suitable forrayon manufacture is to be made having projections on one of itssurfaces and corresponding depressions on the other surface, for thepurpose set forth.

2. A sheet composed of wood pulp from which viscose suitable for rayonmanufacture is 'to be made having corrugations, for the purpose setforth.

3. A sheet composed of wood pulp from which viscose suitable for rayonmanufacture is vto be made having corrugations, said corrugations beingdiagonally arranged in respect to the edges of said sheet, for thepurpose set forth.

4. A sheet composed of cellulosio material from which viscose suitablefor rayon manufacture-is to be made having pro ections on one of itssurfaces and corresponding depressions on the other surface.

' In testimony whereof, we have afixed our signatures to thisspecification.

GALO W. BLANCO. CARLETON HENNINGSEN.

